1. Field of the Invention
The present invention relates to a dielectric resonance device including a cavity and a dielectric core disposed therein, as well as to a dielectric filter, a composite dielectric filter device, a dielectric duplexer, and a communication apparatus, each of which utilizes the dielectric resonance device.
2. Description of the Related Art
The applicant of the present application has filed Japanese patent application Nos. 10-220371 and 10-220372 for inventions in relation to dielectric resonators which are compact and facilitate formation of a multi-stage resonator. In the dielectric resonators of these applications, a substantially parallelepipedic dielectric core is disposed within a substantially parallelepipedic cavity, and the dielectric core is resonated in multiple modes.
Dielectric resonance devices in which a dielectric core is disposed within a cavity in an isolated manner typically employ a structure such that the dielectric core is supported at a predetermined position within the cavity via a support base. FIGS. 16 and 17 shows an example of the structure, wherein FIG. 16 is an exploded perspective view of a dielectric resonance device, and FIG. 17 is a vertical cross section of the dielectric resonance device at the center thereof. In these drawings, reference numeral 3 denotes a parallelepipedic dielectric core, which is fixed to the bottom surface of a cavity body 1 via a support base 4 of low dielectric constant. A cavity lid 2 is placed on the top opened surface of the cavity body 1.
When the dielectric core 3 of the dielectric resonance device resonates in a TM01xcex4xe2x88x92x mode or in a TM01xcex4xe2x88x92y mode, the resonance frequency varies with the capacitance which is present between inner walls of the cavity which face end surfaces of the dielectric core 3, as indicated by a symbol of a capacitor in FIG. 17. Therefore, if the linear expansion coefficients of the dielectric core and the support base differ from that of the cavity, the capacitance present between the peripheral surface of the dielectric core and the inner wall of the cavity will vary with temperature, with resultant variation in resonance frequency. The resonance frequency also varies in accordance with the temperature coefficient of the dielectric core.
FIGS. 18A and 18B are graphs showing such variation in resonance frequency. In FIG. 18A, the horizontal axis represents time, and the vertical axis represents variation in resonance frequency relative to the resonance frequency at 25xc2x0 C. In FIG. 18B, the horizontal axis represents temperature, and the vertical axis represents variation in resonance frequency relative to the resonance frequency at 25xc2x0 C. In this example, when the temperature of the dielectric resonance device is lowered to xe2x88x9230xc2x0 C., the resonance frequency of the TM01xcex4xe2x88x92x mode and the resonance frequency of the TM01xcex4xe2x88x92y mode decrease by 0.5 to 0.6 MHZ, and when the temperature of the dielectric resonance device is raised to +85xc2x0 C., the resonance frequencies of these two modes increase by 0.7 to 0.8 MHZ.
Although the above-described temperature characteristics of the resonance frequencies can be improved through employment of a material of low linear expansion coefficient, such as invar or 42%-nickel iron alloy, this increases cost. Further, when in addition a TE01xcex4 mode of the dielectric core is utilized in a dielectric resonance device having a structure as shown in FIGS. 16 and 17, the temperature characteristic of this mode raises another problem. That is, the resonance frequency of the TE01xcex4 mode does not relate directly to the capacitance between the peripheral portion of the dielectric core and the inner wall of the cavity but depends on the size of the cavity and the temperature coefficient of the dielectric core. In the example case shown in FIG. 18, the resonance frequency of the TE01xcex4 mode increases by about 0.3 MHZ as a result of a temperature decrease to xe2x88x9230xc2x0 C. and decreases by about 0.4 MHZ as a result of a temperature increase to +85xc2x0 C. The directions of these variations are completely opposite those in the case of the TM01xcex4xe2x88x92x mode and the TM01xcex4xe2x88x92y mode. Accordingly, the above-described TM01xcex4 modes differ from the TE01xcex4 mode in terms of temperature characteristic of the resonance frequency, thereby raising a different problem, that the overall frequency characteristic of the resonance device varies with temperature.
In view of the foregoing, the present invention provides a dielectric resonance device which has a stabilized temperature characteristic of a TM-mode resonance frequency, which would otherwise vary due to differences in linear expansion coefficient among a dielectric core, a support base, and a cavity.
The invention further provides a dielectric filter, a composite dielectric filter device, a dielectric duplexer, and a communication apparatus, each of which utilizes the dielectric resonance device.
The present invention also provides a dielectric resonance device with reduced variation in the frequency characteristic with temperature in a multi-mode operation utilizing TM and TE modes, as well as a dielectric filter, a composite dielectric filter device, a dielectric duplexer, and a communication apparatus, each of which utilizes the dielectric resonance device.
The present invention provides a dielectric resonance device comprising: an electrically conductive cavity; a dielectric core fixedly disposed within the cavity via a support base, the dielectric core being capable of resonating in a TM mode; and a capacitance-generation electrode having the same electrical potential as that of the cavity and provided at a predetermined position between an inner wall surface on which the support base is fixed and a support-base attachment surface of the dielectric core through which the dielectric core is attached to the support base, such that a capacitance is produced between the electrode and the support-base attachment surface of the dielectric core.
As a result of employment of this structure, when temperature varies, the size of a gap between the peripheral surface of the dielectric core and the inner wall surface of the cavity and the size of a gap between a circumferential portion of the support-base attachment surface of the dielectric core and the electrode change in directions opposite each other. Therefore, variation in the capacitance between the dielectric core and the cavity is suppressed, so that the resonance frequency of the TM mode is stabilized.
The electrode may be a stepped portion which is provided inside the cavity such that a surface of the stepped portion faces a circumferential portion of the support-base attachment surface of the dielectric core.
In this case, since the stepped portion provided inside the cavity serves as an electrode which faces a circumferential portion of the support-base attachment surface of the dielectric core, the characteristics can be improved without increase in the number of components.
Alternatively, the electrode may be an electrically conductive member, for example a plate, attached to the inner wall surface of the cavity such that the conductive member or plate faces a circumferential portion of the support-base attachment surface of the dielectric core.
In this case, since the electrode is provided through attachment of the conductive member or plate, the structure of the cavity before attachment of the conductive member or plate is simple, and therefore the cavity can be fabricated with ease. Further, the characteristics can be switched or adjusted by selectively changing the shape of the conductive member or plate and/or the manner or location of its attachment.
Alternatively, the electrode may be a member such as a screw which projects toward the interior of the cavity.
In this case, the temperature characteristic of the dielectric resonance device can be optimized with ease through adjustment of the screw.
Preferably, the dielectric core resonates in TM01xcex4 and TE01xcex4 modes at substantially the same resonance frequency; and the shapes and sizes of the dielectric core, cavity, and capacitance-generation electrode are determined such that, when temperature varies, the resonance frequency of the TM01xcex4 mode varies in the same direction as that of the resonance frequency of the TE01xcex4 mode. That is, the resonance frequency of the TE01xcex4 mode does not relate directly to the gap between the peripheral surface of the dielectric core and the cavity or to the gap between a circumferential portion of the dielectric core and the capacitance-generation electrode, but, as best understood, is determined by the size of the cavity and the temperature coefficient of the dielectric core. In view of the above, deterioration of the overall frequency characteristic of the dielectric resonance device, which deterioration would otherwise occur due to temperature variation, is suppressed through a design which renders the direction (polarity) of variation with temperature of the resonance frequency of the TM01xcex4 mode the same as that of the resonance frequency of the TE01xcex4 mode.
When the TM01xcex4 mode and the TE01xcex4 mode are used in a multiplex manner, the temperature characteristic of the resonance frequency of the TM01xcex4 mode becomes substantially the same as that of the resonance frequency of the TE01xcex4 mode, so that deterioration of the frequency characteristic due to temperature variation can be prevented.
The present invention also provides a dielectric filter which comprises the above-described dielectric resonance device; and couplings which couple with the dielectric core of the dielectric resonance device and through which signals are input and output.
The present invention further provides a composite dielectric filter device which comprises a plurality of the above-described dielectric filters.
The present invention further provides a dielectric duplexer which comprises first and second filters, wherein an input port of the first filter is used as a transmission signal input port, an output port of the second filter is used as a reception signal output port, and a common input/output port of the first and second filters is used as an antenna port.
The dielectric filter, the composite dielectric filter device, and the dielectric duplexer of the present invention exhibit excellent stability in terms of frequency characteristic against temperature variation.
The present invention further provides a communication apparatus which comprises the dielectric filter, the composite dielectric filter device, or the dielectric duplexer and which serves as, for example, a communication apparatus at a base station of a mobile communication system.
The communication apparatus of the present invention exhibits excellent stability in terms of communication characteristics against temperature variation, and can be used in a widened temperature range.
Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings.